Implementations of the claimed invention generally may relate to the field of equalizers in digital communication systems, and in particular to the initialization such equalizers.
Equalizers are employed in digital communication systems to remove the distortions in a received signal caused by transmission channels. Such equalizers serve an important function in digital communication systems, especially in wireless communication environments where radio multipath always occurs. In ATSC (Advanced Television Systems Committee) digital broadcast television systems, for example, an 8-VSB signal is transmitted through a traditional 6-MHz bandwidth TV channel with symbol rate at 10.76 MHz. Because of multipath propagation, the received signal at a receiver (e.g., TV set) will be a combination of infinite copies of the transmitted 8-VSB passed through different paths with different arrival time and phase. When the difference of these signal copies propagation distances is larger than 30 meters, which is very common, the received signal is distorted by inter-symbol interference. In practice, the difference of the TV signal propagation distance can be up to several kilometers.
Consequently, an equalizer in ATSC TV set typically has several hundred taps and plays the most important role. Many equalizer strategies have been applied to ATSC TV set products in the market. Among them the decision feedback equalizer is a prevalent choice. The decision feedback equalizer typically includes a feed-forward FIR filter and a feed-back FIR filter. The coefficients of these filters are updated according to an error measurement of the equalizer output signal, and are adaptive to changes in the transmission channel(s). The error measurement may be based on either a known output signal (training mode), or some statistics property (blind mode), or an estimate signal (decision mode). Prior to the coefficient adaptation that characterizes normal equalizer operation, the equalizer coefficients are initialized to suitable values.
Typically, the initial values of the equalizer coefficients are determined from an estimated channel whose impulse response is computed by cross-correlating a known training signal with the received signal. Several approaches have been proposed (e.g., those in US2003/0185295, US02004/179483, US2005/0169361, US2005/0254570, etc.) for generation of the equalizer initial coefficients by using an estimated channel. Based on the equalizer structure used, these approaches convert the equalizer computation into an optimization problem and solve the optimization problem by some methods such as MMSE. Due to the computation complexity of the optimization problem, this may involve a large amount of vector and matrix addition and multiplication.
If the initialization computation were performed by software, then a powerful CPU and large memory would be needed. If performed by hardware, specific circuits may be implemented for the initialization computation. Given that equalizer coefficient initialization is done only once for setting up the equalizer coefficients, smaller circuits for equalizer initialization may be desirable.